1. Field of the Invention
The present invention relates to a hybrid integrated circuit and, more particularly, to a hybrid integrated circuit for operation at a high frequency and a high output level.
2. Description of the Related Art
FIG. 4 shows the construction of a typical hybrid integrated circuit for operation at a high frequency and a high output level. The circuit has an insulating substrate 1 on which are formed a plurality of conductor patterns 2 to 8. A semiconductor chip 9 is bonded to the conductor pattern 2 by, for example, soldering. The semiconductor chip 9 has a grounding line formed on the surface thereof where it is bonded to the conductor pattern 2 and internal electrodes formed on the other surface thereof. The grounding line is connected to the conductor pattern 2 as a result of bonding of the semiconductor chip 9 to the conductor pattern 2. The internal electrodes on the other surface of the semiconductor chip 9 are respectively connected to the conductor patterns 3 and 4 through thin metal wires 10. Circuit elements such as chip capacitors 11, 12 are connected between the conductor patterns. Leads 13 are connected at one of their ends to the conductor patterns 6 to 8 while the other ends of the leads 13 are led externally from the insulating substrate 1. A grounding thin conductor film 14 such as of Ag/Pt or Au is formed over the entire area of the reverse side of the insulating substrate 1. The thin conductor film 14 is electrically connected to the conductor pattern 2 via a through hole connection 15.
The insulating substrate 1 is mounted on a grounding and heat-radiating metallic plate 16 by bonding the thin conductor film 14 to the metallic plate 16. In addition, mounted on the metallic plate 16 is a cap 17 which is made of plastic and which covers the insulating substrate 1, protecting the insulating substrate 1.
A high-frequency current is input to the hybrid integrated circuit through the leads 13 to operate the hybrid integrated circuit. As a result, the semiconductor chip 9 generates heat which is transmitted via the conductor pattern 2, the through hole connection 15 and the thin conductor film 14 to the metallic plate 16 so as to be radiated therefrom. Thus, in the conventional hybrid integrated circuit, a single insulated substrate 1 is mounted on the metallic plate 16 and a single circuit is formed on the insulating substrate 1.
In general, an electronic device comprises a plurality of circuits. It is often convenient and, hence, desirable to pack two or more of these circuits in a single package to reduce the size of the whole electronic device. For instance, a power amplifier circuit and a driver circuit for driving the power amplifier circuit are preferably integrated in a single hybrid integrated circuit rather than being arranged separately and connected together. The result is a reduction in the size of the apparatus and an improvement in its reliability.
Previously, for the purpose of forming a hybrid integrated circuit of a higher density, it was necessary that a plurality of circuits be mounted on a comparatively large metallic plate. This goes quite contrary to the demand for reduction in the size of the electronic device. Another problem encountered with the described conventional arrangement arises from the use of a dielectric material such as plastic as the material for the cap 17 which covers and protects the insulated substrate 1. Namely, such a dielectric material tends to allow mutual electromagnetic interference between the hybrid integrated circuit and external circuits, particularly when the hybrid integrated circuit is designed for operation at a high frequency and a high output level. This reduces the reliability of the electronic device. For these reasons, it has been necessary to shield the electronic device by a conductive material.